Blue-violet semiconductor laser devices in the 400-nanometer wavelength band are used for next generation DVD (digital versatile disc) applications. Gallium nitride and other nitride semiconductors are suitable as semiconductors emitting light in this wavelength band.
There is a disclosed technology of a nitride semiconductor laser device in which dielectric reflecting films are formed on both facets of a stripe serving as an optical resonator in order to achieve high power and reliability (JP 2004-006913A). This disclosed technology is characterized in that the dielectric reflecting film is formed as a multilayer film containing two materials selected from SiO2, TiO2, and ZrO2.
However, a reflecting film of such composition has an excessively different linear expansion coefficient relative to gallium nitride based semiconductors. This results in insufficient adhesion between the films, and the reflecting film is likely to peel off. Consequently, characteristics variation and reliability degradation may occur.
In nitride semiconductors, non-radiative recombination is likely to occur due to a deep level formed particularly in the vicinity of a facet. The non-radiative recombination decreases carriers at the facet and increases optical absorption. This causes temperature increase and bandgap shrink in the vicinity of the facet, which further increases optical absorption. This positive feedback leads to COD (Catastrophic Optical Damage), and therefore the available maximum optical power decreases.